1. Field of the Invention
This invention lies in the field of polyols useful in formulating resin prepolymer blends for reaction with organic isocyanates to produce polyurethane and/or polyurethane-polyisocyanurate cellular polymers, and, more particularly, in the field of phthalate polyester polyols which self-compatibilize with fluorocarbon blowing agents.
2. Prior Art
Aromatic polyester polyols are coming into widespread usage in the manufacture of polyurethane and polyurethane-polyisocyanurate foams. Such polyester polyols are attractive because they tend to be low in cost, yet can produce rigid cellular polymers of excellent properties adapted for many end use applications.
One class of aromatic polyester polyols which has recently become commercially available comprises esters produced by esterifying phthalic acid or phthalic acid anhydride with an aliphatic polyhydric alcohol. For example, a diethylene glycol phthalate is available commercially from Stepan Company, Northfield, Ill. Such liquid product has a desirably low viscosity, a desirably high aromatic ring content, and a desirably low acid number. Even though such product typically has a reactive hydrogen functionality of less than about 3, it catalytically reacts well with organic isocyanates to produce, for example, rigid cellular polyurethane-polyisocyanurate polymer that can have excellent characteristics, such as compressive strength, tumble friability, and burn char.
One problem generally with such aromatic polyester polyols is that they characteristically are poorly compatible with fluorocarbon compounds of the type conventionally used as blowing agents to make such cellular polymers.
The usual solution to this problem has been to admix with such a polyol a compatibilizing agent in an amount sufficient to produce a resulting mixture with a desired amount of compatibility (solubility) for fluorocarbons. For examples, Koehler et al U.S. Pat. No. 4,246,364 use a class of amide diols, while Wood U.S. Ser. No. 622,670 filed June 20, 1984 (now allowed U.S. Pat. No. 4,529,744) uses a combination of relatively high molecular weight propoxylate ethoxylate compounds with amine and/or amide diol compounds. The amide diols employed by Wood are similar to those taught by Koehler et al. The propoxylate ethoxylate compounds employed by Wood are, in fact, similar to those employed in one preferred mode of practicing the present invention, as hereinbelow described.
The necessity to compound a fluorocarbon compatibilizing agent with aromatic polyester polyol means an extra cost in the formulation of a so-called resin prepolymer blend. Such resin prepolymer blends are conventionally employed in the trade for reaction with organic isocyanates to produce polyurethane and/or polyurethane-polyisocyanurate cellular polymers. Resin prepolymer blends are uniform, homogeneous liquid compositions comprised of polyol, urethane-forming and/or isocyanurate-forming catalyst, fluorocarbon blowing agent, other optional additives, and, in the case of aromatic polyester polyols, a fluorocarbon compatibilizing agent, as is well known to those skilled in the art. A desired quantity of a compatibilizing agent is blended with an aromatic polyester polyol before such fluorocarbon is added, and such a blending step itself adds to the cost of resin prepolymer blend manufacture.
However, the cost of a compatibilizing agent is even more significant. Moreover, the costs of such an agent are escalating. For example, the cost of the cochin oil, which is used as a starting material to make the amide diol above identified, increased by approximately 60 percent in price in 1984. Unless the cost of producing resin prepolymer blends of aromatic polyester polyols can be controlled and maintained at economically competitive levels, aromatic polyester polyols will not have a commercial place in this field.
There is a need for fluorocarbon compatibilized aromatic polyester polyols which not only are economical to produce, but also are convertible into cellular foams having excellent properties.
Aromatic polyester polyols, especially phthalate polyester polyols, are producible by esterifying aromatic polycarboxylic acids with polyols, as is known. The idea of somehow modifying into the components which would result in a polyol that is directly compatible (self-compatibilized) with fluorocarbons is certainly attractive. Not only would this avoid the need for a separate compatibilizing agent blending step, but also this would avoid the cost of an added compatibilizing agent.
Bernstein U.S. Pat. No. 3,298,974 provides a prior art attempt to prepare an aromatic polyester polyol which would be compatible with fluorocarbons. The Bernstein teachings recognize the desirability of using phthalic anhydride as a dicarboxylic acid for use in making a polyester polyol, but, for his esterification polyol, he employed only polyols containing at least 3 hydroxyl groups per molecule. To avoid the resulting high viscosity problems, use of an aliphatic dicarboxylic acid e.g., adipic acid, to replace portions of the phthalic anhydride is mentioned (see column 1, lines 20-45) as prior art. However, in the '964 patent, Bernstein describes polyester polyols produced by reacting a polycarboxylic acid of which aromatic dicarboxylic acid constitutes at least 25% by weight with an ethylene oxide adduct of an aliphatic polyhydric alcohol initially containing from 3 to 6 hydroxyl groups so that the resulting adduct contained 10 to 22 milliequivalents per gram of hydroxyl groups. Such a polyester polyol product was said to display increased fluorocarbon solubility and was said to be formed in the presence of some "higher molecular weight monocarboxylic or fatty acid" (see column 4, lines 25-43). Bernstein never taught low molecular weight diols for reaction with phthalic anhydride. The Bernstein polyester polyols are evidently not suitable for use in producing cellular polyurethane-polyisocyanurate type polymers of commercially acceptable quality. Apparently, these Bernstein products have never been successfully commercialized.
Windemuth et al British Pat. No. 908,337 describes "reacting at least one polyhydroxyl and/or polycarboxylic compound with a molecular weight greater than 300 . . . with more than twice the quantity of polyisocyanate which is required for reaction" with the objective being to employ "a large excess of polyisocyanate" (see page 1, column 2, lines 62-84). Within "another large group of suitable starting materials (that) comprises linear or branched polyesters containing OH and/or COOH groups" phthalic acid and diethylene glycol are listed among many other compounds, and it is then stated that: "Polyesters . . . obtained from the aforesaid . . . can of course also be modified with monofunctional alcohols, amines, carboxylic acids, or saturated or unsaturated fatty acids, such as for example oleic acid." (see page 3, column 1, line 57 through column 2, line 90). Elsewhere it is indicated that such modifiers are added to reduce viscosity (see page 2, column 1, lines 18-46). No discussion of fluorocarbon compatibility whatever appears in Windemuth et al, and no phthalate polyester polyols made only of phthalic anhydride, low molecular weight diol, and such modifier is shown. The only phthalate containing polyester polyol illustrated appears in Example 35, and this polyol is "a mixture of 70 parts by weight of a polyester of 3 moles of polypropylene glycol (OH number 270) and 2 moles of adipic acid (acid number 2, OH number 84), 30 parts by weight of a polyester of 2 moles of phthalic acid anhydride, 1 mole of adipic acid, 1 mole of oleic acid and 5.3 moles of trimethylolpropane (OH number 353, acid number 0.5)" (see page 19, column 2, line 24 through page 20, column 1, line 5). The exemplified Windemuth et al aromatic polyester polyol systems are evidently not suitable for use in producing cellular polyurethane-polyisocyanurate type polymers of commercially acceptable quality, and apparently such have never been successfully commercialized.
So far as is known, no one has heretofore produced a class of phthalate polyester polyols which is both fluorocarbon self-compatibilizing, and also has a combination of low viscosity, low acid number, low reactive hydroxyl functionality (less than 3), and high aromatic ring content. Such a phthalate polyester polyol can be formulated into a resin prepolymer blend and then reacted with organic isocyanate to produce cellular polyurethane-polyisocyanurate type polymers of generally commercially acceptable quality.